Pressure vessels are constructed in many forms and sizes for confining liquids and/or gases in various applications. A common characteristic of such vessels is the provision of an opening therein, with an attached closure means, to give access to the interior of the vessel for cleaning, inspection, servicing, and installation of internal parts. A safety problem is thus presented: serious or fatal injuries can occur (and have occured) when an attempt is made to open the closure means before the vessel is depressurized. Thus there is a need for apparatus which renders it substantially impossible to open the closure means of a pressure vessel until the internal pressure has been bled off.
While the safety problem just outlined inheres in pressure vessels generally, it is presented in a more acute form in those pressure vessels having more than one pressure compartment therein, because failure to depressurize any one of the compartments will create an unsafe condition when an attempt is made to open the vessel. A worker who has depressurized one compartment may easily misconceive that the entire vessel is depressurized and safe to open.
An example of a multi-compartment pressure vessel, and one to which the present invention is particularly applicable, is a pulsation stabilizer of the general kind shown and described in my prior U.S. Pat. No. 3,376,898 issued Apr. 9, 1968. Pulsation stabilizers are employed to dampen destructive pressure surges in lines at the inlets and outlets of pumps for both liquids and gases. Typically, such stabilizers comprise an open-ended, usually cylindrical, case with fittings for admitting the fluid to be damped into the case. The open end of the case is normally closed by a closure plate having a gas fillable cartridge mounted thereon. When the closure plate is placed over the open end of the case, the gas cartridge extends into the case and occupies a significant portion of its volume. Typically, the closure plate has two bores therethrough, one to be equipped with valve means for pressurizing and depressurizing the gas cartridge and the other to be equipped with valve means for bleeding off pressure in the case exteriorly of the cartridge. In a typical stabilizer, the closure plate is held in pressure-tight engagement with the open end of the case by closure means, which may take various forms, such as a hold-down nut threaded on to the case, a set of clamps, nuts engaging studs on the case, etc.
When a worker approaches a stabilizer vessel to service it, he first closes an external valve in the line between the pump and the vessel. This isolates the vessel from the pressure source, but does not depressurize it. It is essential that both of the above mentioned valve means be actuated to depressurize both the case and the gas cartridge, before the closure means can safely be actuated to force the closure plate from the case.